A circuit device typically communicates electrically through “interconnects.” Interconnects are so named because they allow circuit devices to electrically connect with other circuit elements. Interconnects often include an arrangement of conductive wires to electrically connect a circuit device. Use of circuit devices that are small or densely packed (“dense circuit devices”), however, can be limited because of difficulties in bonding interconnects to such devices.
By way of example and referring to FIG. 1, a side-section view of a fragment of a dense circuit device is indicated generally by reference numeral 102. The device 102 includes electrical bond pads 104. The pads 104 have a width 106 and are generally separated from each other by a space 108. The smaller or denser the device 102, typically the less the width 106 and the space 108. As the width 106 and space 108 of the pads 104 get smaller and smaller with production of smaller or denser circuit devices, forming interconnections among and between these devices becomes more and more difficult.
Again referring to FIG. 1, a side-section view of a fragment of a conventional interconnect is indicated generally by reference numeral 110. The conventional interconnect 110 is typically made of different materials than the device 102, often because the materials used in the device 102 are relatively expensive. Also typically, to bond the conventional interconnect 110 to the pads 104 of the device 102, heat is used.
But a significant problem can occur when using heat to bond the conventional interconnect 110 to the pads 104 of the device 102. If the coefficient of thermal expansion (called “CTE”) for the conventional interconnect 110 and the device 102 are even slightly different, wires 112 of the conventional interconnect 110 may not match up with the pads 104 when they are heated for bonding. When the width 106 or the space 108 is very small, the wires 112 may completely miss the pads 104 or line up with the wrong ones.
By way of example and referring to FIG. 2, a side sectional view of the device 102 and the conventional interconnect 110 when each is heated is shown. Both the device 102 and the conventional interconnect 110 are shown expanded in this example, but the expansion of the conventional interconnect 110 does not match the expansion of the device 102. As shown, the wires 112 do not properly match up with the pads 104. When the width 106 or the space 108 is very small, such as less than 100 nanometers, and the device 102 or the interconnect 110 is significantly larger than the width 106 or the space 108, a difference in coefficient of thermal expansion between the device 102 and the conventional interconnect 110 may cause the pads 104 and the wires 112 to not match up with each other. If, for instance, a coefficient of thermal expansion between the device 102 and the interconnect 110 is different by five percent, the wires 112 and the pads 104 may miss each other by hundreds and hundreds of nanometers. This failure of conventional heat bonding may make it impractical or unusable for interconnecting to some dense circuit devices.
Other prior-art techniques for bonding an interconnect to a circuit device can also cause various problems. Eutectic bonding, for instance, can require use of specific, non-optimal materials for the wires 112 and/or the bond pads 104. These non-optimal materials can limit the usability of the dense circuit device 102, because they may not be highly conductive, which is especially important with small-scale interconnects used with dense circuit devices. This eutectic bonding technique can also fail by providing too weak an electrical connection between the bond pads 104 and the wires 112.
Further, these and other typical techniques for electrically bonding the conventional interconnect 110 to the circuit device 102 include mechanical bonding of the wires 112 to the bond pads 104. This can cause a significant problem. If the device 102 and the conventional interconnect 110 are subject to heat, CTE mismatch of the wires 112 to the bond pads 104 can cause the mechanical bonding between them to fail. This mechanical failure often causes the electrical connection between the wires 112 and the bond pads 104 to also fail.
There is, therefore, a need for a technique for bonding interconnects to dense circuit devices that reduces CTE-related problems, and is reliable, less expensive, and/or more production-friendly than permitted by present-day techniques.
The same numbers are used throughout the disclosure and figures to reference like components and features.